Light projected from an active lighting means to an object is reflected by the object, and a light spot is produced on a light-sensitive element by the light reflected from the object. The distance to the object is determined by detecting the position of the light spot on the light-sensitive element. The light-sensitive element for receiving the reflected light from the object has formed on a portion of a surface thereof an insensitive zone which has the same width or the same area as the light image produced by the reflected light and the light-sensitive element moves on an image plane in a certain relationship with the distance to the object whereby a change in a photoelectric output of the light-sensitive element is detected to detect the distance to the object.

The disclosed position measuring device includes a position sensitive detector and a processing circuit therefor. The position sensitive detector includes two terminals carrying signals that vary oppositely according to the incident light. A switch connected to one terminal opens and closes the one terminal, and a signal processor processes one output of the position sensitive detector when the switch is opened and another output of the position sensitive detector when the switch is closed so as to produce normalized light/point position information. A control controls the signal processing circuit and the switch.

A measuring distance apparatus for measuring a distance to an object in accordance with an incident position of a reflected light of a signal light projected to the object is disclosed. It comprises photosensing means for sensing the signal light having a plurality of photo-electric converters each having a first electrode connected to a first range of potential and a second electrode connected to the second electrode of other photo-electric converter by a resistive wire, means for connecting at least one point on the resistive wire to a second range of potential which is different from the first range of potential by a conductive wire having a lower resistance than the resistance of the resistive wire, switching means for connecting and disconnecting the conductive wire, and detection means connected to the resistive wire at a point farther from or closer to the incident point of the signal light varying with a distance to the object from a point on the resistive wire to which the conductive wire is connected, for detecting an output status at that point. The incident position of the signal light is detected from a change of the output status of the resistive wire connected to the detection means so that the distance to the object is detected.

A semiconductor light position detector for a rangefinder which projects a light beam onto an object and receives a reflected light beam from the object to measure a distance to the object. A portion of the light-receiving surface of the detector on which the reflected beam will not form a light spot is partially covered with a member that blocks unwanted light. Thus, the malfunctions caused by the flare component of the light from the light projector and the malfunctions due to increases in the shot noise under a high illuminance are reduced greatly.

Disclosed is a computer-assisted method for analyzing the surroundings of a display device. At least two different patterns are displayed successively on a display device connected to a computer. A camera is also connected to the computer and is directed towards objects in front of the display device. Each time a pattern is displayed on the display device, at least one image of the surroundings is captured. The captured images are combined to create a difference image. The difference image is analyzed to interpret the objects in the surroundings. For example, calculations may be performed to segment the foreground from the background of the surroundings or to estimate the range (distance) of the objects from the display device. An apparatus for performing this computer-assisted method is also disclosed.